March is a good time for starting potted plants that have overwintered in your greenhouse into summer growth. Although greenhouse temperatures vary widely at this time of the year, most of the hardest frosts will be over and new growth should not be killed back if you keep the vents and doors closed at nights.
Plants that don’t need repotting just need tidying up, watering and maybe feeding. For those that needrepotting the procedure is simple. Tip a plant out of its existing pot. A few plants like Amaryllis need to be kept confined, but most will probably need bigger pots this time if they needed frequent watering and feeding last year. Other warning signs of pot-binding are roots growing out the top or bottom of the pot, and a solid mass of roots and little soil when you turn a plant out of its pot. Don’t use a much larger pot; about two centimetres of soil or compost all round is enough for roots to fill before it gets stale and soggy.
Remove any loose material between the plant roots and use it as mulch in the garden. You can pot up plants with peat compost, soil or a mixture of both. Pure peat is expensive, hard to wet when fully dry and favours vine weevils. Stand the plant in a part-filled pot so that its original soil surface is about a centimetre below the top and fill up to there with slightly damp, gently firmed potting medium. The space between the surface and the top of the pot is to hold water poured in when watering. Water the pot/s right away, and if the plant roots have been disturbed much (like rooted cuttings and divided plants) give some shade for a week or so.